Multiple carrier modulation (MCM) techniques, e.g., orthogonal frequency division multiplexing (OFDM), are generally known.
Like other communication techniques, a received MCM (again, e.g., OFDM) signal is subject to noise introduced between the transmitter and the receiver. This noise includes additive white Gaussian noise (AWGN) and impulse noise. Typically, non-negligible impulse noise sources are electronic devices near the receiver that exhibit large local magnetic fields induced by switching large amounts of current, e.g., during energization of: motors that move an elevator carriage; motors and/or an exposure device in a photocopier machine, etc.
It is known to estimate (and attempt to remove) impulse noise content in the received multi-carrier-modulated (MCM) signal prior to the signal being equalized (a “pre-EQ signal). FIG. 1 is a block diagram depicting a typical MCM system 100 that includes components for removing impulse noise from a pre-EQ signal, according to the Background Art. For simplicity, only a portion of the system 100 is depicted, as is indicated by the ellipses ( . . . ).
In more detail, system 100 includes the following serially-connected components: a down converter 126; a clipping unit 101; and a guard-interval removing unit 130. Clipping unit 101 includes: a variable gain amplifier 180; a clipping device 182; an analog-to-digital converter (ADC) 184; a feedback loop formed of a power estimation unit 186 operating upon the output of ADC 184; and a threshold calculation unit 188 that operates upon the power estimate from unit 186 and provides a threshold control signal to amplifier 180. Details concerning FIG. 1 can be found in published European patent application, publication No. EP 1011235. Magnitudes of the pre-EQ signal greater than what is typically expected are detected and either clipped to a threshold level by clipping device 182, or to zero (e.g., published European patent application, publication No. EP 1043874).